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Monica Okon, Yanhui Ma, Jun Liu, Cynthia J Roberts; Correction of Optical Distortion in Scheimpflug Imaging of a Deformed Cornea at Maximum Concavity when Loaded by an Air-Puff. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2141.
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To determine the corrected corneal thickness and anterior chamber depth of a cornea’s deformation response to an air-puff, imaged with Scheimpflug geometry
The Fink method (Fink, J Biomedical Optics, 2005) for optical/refractive correction of Scheimpflug images via ray tracing was implemented in Matlab. The edges of the anterior and posterior corneal surface of a sample CorVis ST exam (Oculus, Wetzlar, Germany) were exported. The observed difference between these exported edges was taken as the uncorrected central corneal thickness (CCT). The anterior surface of the crystalline lens was extracted via an edge detection algorithm in Matlab. The Fink method was then applied to calculate the corrected CCT and anterior chamber depth (ACD) of the pre-deformation and maximum concavity state of the cornea’s response to the air puff. The method was validated against the pachymetry measurement from the same CorVis ST exam.
In the two states of the cornea’s deformation response, the results showed that the corrected CCT and ACD were larger than the uncorrected values. The uncorrected and corrected CCT were 422 μm and 648 μm, respectively. The reported CCT from the CorVis ST was 638 μm (1.57% error). The uncorrected and corrected radius of curvature of the posterior corneal surface were 5.4736 mm and 4.7196 mm, respectively. The uncorrected and corrected ACD at the corneal apex were 1.9 mm and 2.7 mm, respectively.
The refractive and Scheimpflug distortion in a CorVis ST image can be corrected using Fink’s method. After correction for both distortions, the corrected CCT and ACD were greater than the observed values in the Corvis ST images. Implementation of Fink's method of correction demonstrates that the apparent forward motion of the lens during corneal deformation is a result of optical distortion.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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